The present invention relates to an apparatus for recording and reading information on a magnetic disk provided with a plurality of recording tracks which are concentric with respect to the axis of rotation of the disk.
The apparatus is of the type comprising means for rotating the magnetic disk, at least one magnetic head for recording and reading the information on the recording tracks, means for translating the magnetic head radially with respect to the disk and for positioning it on a selected recording track, and means for controlling the translation means.
In accordance with a known technique, in order to achieve a high degree of packing of the recording tracks, burst information is prerecorded on each of the tracks; when such information is read by the magnetic head, it is such as to give rise to the generation of electrical signals which are indicative of precise positioning of the head with respect to the selected track, or the error in positioning that may occur as between the head and the track.
An apparatus is known, which is provided with two stepping motors connected to a carriage on which the magnetic recording and reading head is mounted. One of the stepping motors, which has an elementary step equal to the radial distance between one recording track and the other is controlled in conventional manner, in a stepwise mode, to cause translatory movement of the magnetic head radially with respect to the disk. The second one of the stepping motors however has a much smaller elementary step and is operable to produce micro-movements of the carriage for the purposes of correcting the position reached by the carriage by operation of the first motor.
Since such apparatus, uses two stepping motors, one for coarse positioning and the other for fine positioning, it is inevitably very expensive.